需求

最近项目中要加页面缓存功能，因为网站内存有限，页面只能存在硬盘中，ASP.NET Core提供了ResponseCache中间件，但是只支持内存缓存，我们需要将缓存存在页面文件中
并且如果产品、系列在后台被修改，需要尽可能实时的修改页面
所以需要通过ResponseCache中间件源码查看如何扩展

源码

ResponseCachingMiddleware构造函数

        internal ResponseCachingMiddleware(
            RequestDelegate next,
            IOptions<ResponseCachingOptions> options,
            ILoggerFactory loggerFactory,
            IResponseCachingPolicyProvider policyProvider,
            IResponseCache cache,
            IResponseCachingKeyProvider keyProvider)
        {
            _next = next;
            _options = options.Value;
            _logger = loggerFactory.CreateLogger<ResponseCachingMiddleware>();
            _policyProvider = policyProvider;
            _cache = cache;
            _keyProvider = keyProvider;
        }

IResponseCache：提供缓存的读取和写入，框架中只提供了一个内存缓存的实现类，如果需要将缓存写入其他位置，可实现此接口

    internal interface IResponseCache
    {
        IResponseCacheEntry? Get(string key);
        void Set(string key, IResponseCacheEntry entry, TimeSpan validFor);
    }

看到这就知道，如果需要使用其他方式缓存接口内容，需要实现此接口

MemoryResponseCache

IResponseCache接口的实现类

    internal class MemoryResponseCache : IResponseCache
    {
        private readonly IMemoryCache _cache;

        internal MemoryResponseCache(IMemoryCache cache)
        {
            _cache = cache ?? throw new ArgumentNullException(nameof(cache));
        }

        public IResponseCacheEntry? Get(string key)
        {
            var entry = _cache.Get(key);

            if (entry is MemoryCachedResponse memoryCachedResponse)
            {
                return new CachedResponse
                {
                    Created = memoryCachedResponse.Created,
                    StatusCode = memoryCachedResponse.StatusCode,
                    Headers = memoryCachedResponse.Headers,
                    Body = memoryCachedResponse.Body
                };
            }
            else
            {
                return entry as IResponseCacheEntry;
            }
        }

        public void Set(string key, IResponseCacheEntry entry, TimeSpan validFor)
        {
            if (entry is CachedResponse cachedResponse)
            {
                _cache.Set(
                    key,
                    new MemoryCachedResponse
                    {
                        Created = cachedResponse.Created,
                        StatusCode = cachedResponse.StatusCode,
                        Headers = cachedResponse.Headers,
                        Body = cachedResponse.Body
                    },
                    new MemoryCacheEntryOptions
                    {
                        AbsoluteExpirationRelativeToNow = validFor,
                        Size = CacheEntryHelpers.EstimateCachedResponseSize(cachedResponse)
                    });
            }
            else
            {
                _cache.Set(
                    key,
                    entry,
                    new MemoryCacheEntryOptions
                    {
                        AbsoluteExpirationRelativeToNow = validFor,
                        Size = CacheEntryHelpers.EstimateCachedVaryByRulesySize(entry as CachedVaryByRules)
                    });
            }
        }
    }

IResponseCachingKeyProvider

缓存key提供器，后台修改产品数据，我需要找到对应的页面文件，所以缓存key也必须由我生成，比如以下格式：product_001_参数哈希

IResponseCachingPolicyProvider、ResponseCachingPolicyProvider

缓存策略,内部几个方法用来判断是否应该使用缓存
比如：必须是get、head请求，且Header中没有Authorization，才取缓存

ResponseCachingStream

Response.Body流的装饰器

ASP.NET Core - ResponseCache源码分析【未完成】